Negative current collector for lithium metal battery, method for manufacturing the same, and lithium metal battery comprising the same

Abstract

The present invention relates to a negative current collector for a lithium metal battery, a method of preparing the same, and an electrode assembly and a lithium metal battery comprising the same, the current collector comprising a metal current collecting substrate and a coating layer formed on at least one surface of the metal current collecting substrate, the coating layer comprising a ferroelectric, a metal material capable of alloying with lithium, a conductive material, and a binder.

Description

TECHNICAL FIELD

[0001] Cross Reference to Related Applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2020-0168163, filed December 4, 2020, and Korean Patent Application No. 10-2021-0170445, filed December 1, 2021, the disclosures of which are incorporated herein in their entireties by reference.

[0003] The present disclosure relates to a negative current collector for a lithium metal battery, a manufacturing method thereof, and a lithium metal battery including the same. BACKGROUND

[0004] All of the negative electrodes of lithium secondary batteries currently available on the market use graphite, but as the development of high-performance secondary batteries having high capacity density and output is on the rise, there are increasing attempts to use lithium metal as a negative electrode.

[0005] First, the theoretical capacity of graphite is small, 372 mAh / g, when fully charged with Li, and the lithium ion conductivity is low, 10 -12 ~ 10 -14 cm 2 · s -1 , thereby achieving a low capacity of less than 30% with respect to the theoretical capacity at 2C rate. For the use of graphite as a negative electrode in high-performance secondary batteries requiring unit volume capacity and high output, the electrochemical properties of graphite itself are not excellent, and thus it is not suitable for use as a next-generation battery negative electrode material.

[0006] Second, in the case of graphite, the types of electrolytes that can be stably used are limited. Graphite is an interlayer material that forms intercalation compounds with lithium ions as well as anions and solvent molecules. Generally, when a propylene carbonate (PC) liquid electrolyte is used, the co-intercalation phenomenon in which lithium ions and solvent molecules simultaneously enter the inside of graphite induces the exfoliation of graphene layers of graphite, and the capacity reduction caused thereby gradually accelerates, causing problems in long-term use.

[0007] On the other hand, unlike graphite, lithium metal does not have the above problems. The theoretical capacity of lithium metal (3862 mAh / g) is more than 10 times that of graphite, and even at a current density of 2.0 mA / cm 2 The deposition / desorption efficiency of lithium metal is also more than 90% under the above current density conditions, and thus it can be used as a negative electrode of a high-performance secondary battery.

[0008] However, metal lithium has a porous structure due to lithium metal dendrite growth on the metal surface during repeated charging and discharging, short circuits, and generation of lithium fine powder called dead Li, which causes problems in safety and long-term life characteristics. The formation of lithium metal dendrites is generally described by a sand time model, and a rapid decrease in the concentration of lithium ions present on the lithium metal surface and the resulting charge imbalance of cations and anions trigger the growth of lithium metal dendrites. These problems can be alleviated by a ceramic layer or graphene coating on the lithium metal surface, but it is limited to a method of physically suppressing lithium metal dendrite growth. In order to effectively suppress lithium metal dendrites, it is necessary to analyze from the nucleation stage to the growth stage of lithium metal dendrites, and it is necessary to develop a negative current collector capable of adjusting the same. SUMMARY

[0009] TECHNICAL PROBLEM

[0010] The present disclosure aims to provide a negative current collector for a lithium metal battery that suppresses dendrite formation by adjusting the lithium ion concentration and nucleation seed sites around the negative current collector, and exhibits uniform Li growth behavior and improved electrochemical performance; and a manufacturing method thereof.

[0011] Another object of the present disclosure is to provide a lithium metal battery comprising the negative current collector.

[0012] TECHNICAL SOLUTION

[0013] According to one embodiment of the present disclosure, a negative current collector for a lithium metal battery is provided, the negative current collector comprising: a metal current collector substrate, and a coating layer formed on at least one surface of the metal current collector substrate, the coating layer containing a ferroelectric, a metal material capable of alloying with lithium, a conductive material, and a binder.

[0014] Here, the metal current collector substrate can be one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper subjected to surface treatment with a dissimilar metal, stainless steel subjected to surface treatment with a dissimilar metal, and an aluminum-cadmium alloy, and specifically, it can be a metal containing copper.

[0015] In one specific embodiment, based on 100 parts by weight of the coating layer, the coating layer can contain 70 to 89 parts by weight of the ferroelectric, 3 to 10 parts by weight of the metal material alloying with lithium, 3 to 10 parts by weight of the conductive material, and 5 to 20 parts by weight of the binder.

[0016] In one embodiment, the ferroelectric can be at least one selected from the group consisting of organic ferroelectrics containing a polymer while also containing BaTiO3, KNbO3, NaTiO3, KTaO3, Pb(Zr,Ti)O3, SrBiTa2O9, BiTiO 12 , LiTaO3, LiNbO3, WO3, KH2PO4, or NaKC4H4O6·4H2O.

[0017] In one embodiment, the metal material capable of alloying with lithium can be at least one selected from the group consisting of Si, Ge, Sn, Pb, Bi, Sb, As, P, Au, Ag, Zn, Al, and oxides thereof, and in particular, it can be at least one selected from the group consisting of Si, Ge, and oxides thereof.

[0018] In this case, the particle size (D50) of the metal material capable of alloying with lithium can be 10 nm to 10 μm.

[0019] The binder can be a polyacrylic acid (PAA) aqueous binder.

[0020] In one embodiment, the coating layer can be formed to a thickness of 1 to 10 μm.

[0021] According to another embodiment of the present disclosure, there is provided a method of manufacturing the negative electrode current collector, the method including the steps of:

[0022] (a) mixing a powdered ferroelectric, a metal material capable of alloying with lithium, and a conductive material to prepare a mixture;

[0023] (b) mixing an aqueous binder with the mixture to prepare a coating slurry;

[0024] (c) applying the coating slurry to the metal current collector substrate; and

[0025] (d) subjecting the metal current collector substrate coated with the coating slurry to primary drying in an air atmosphere, and to secondary drying in a vacuum atmosphere.

[0026] In one embodiment, the ferroelectric can be at least one selected from the group consisting of organic ferroelectrics containing a polymer while also containing BaTiO3, KNbO3, NaTiO3, KTaO3, Pb(Zr,Ti)O3, SrBiTa2O9, BiTiO 12 , LiTaO3, LiNbO3, WO3, KH2PO4, or NaKC4H4O6·4H2O.

[0027] In one embodiment, the metal material capable of alloying with lithium can be at least one selected from the group consisting of Si, Ge, Sn, Pb, Bi, Sb, As, P, Au, Ag, Zn, Al, and oxides thereof.

[0028] The aqueous binder can be a polyacrylic acid (PAA) binder.

[0029] According to still another embodiment of the present disclosure, there is provided a lithium metal battery, the battery comprising: an electrode assembly comprising a negative electrode in which Li metal is deposited on a negative current collector according to the above-described embodiment, a positive electrode, and a separator interposed between the negative electrode and the positive electrode; and a lithium nonaqueous electrolyte. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a schematic diagram of Li deposition on a negative current collector according to one embodiment of the present disclosure;

[0031] Figure 2 is an SEM photograph of the upper surface of a coated negative current collector according to Example 1;

[0032] Figure 3 shows the shape of Li deposition on a negative current collector according to Comparative Example 3;

[0033] Figure 3 1-1 of FIG. 1 is an image taken by SEM after Li deposition for 1 hour at a current density of 0.5 mA / cm 2

[0034] Figure 3 1-2 of FIG. 1 is an image taken by SEM after Li deposition for 8 hours at a current density of 0.5 mA / cm 2

[0035] Figure 3 2-1 of FIG. 2 is an image taken by SEM after Li deposition for 7 minutes and 30 seconds at a current density of 4.0 mA / cm 2

[0036] Figure 3 2-2 of FIG. 2 is an image taken by SEM after Li deposition for 1 hour at a current density of 4.0 mA / cm 2

[0037] Figure 4 shows the shape of Li deposition on a negative current collector according to Example 1;

[0038] Figure 4 1-1 of FIG. 1 is an image taken by SEM after Li deposition for 1 hour at a current density of 0.5 mA / cm​​​​2 an image taken by SEM after Li deposition for 1 hour at a current density of 0.5 mA / cm

[0039] Figure 4 1-2 of Comparative Example 1 is an image taken by SEM after Li deposition for 8 hours at a current density of 0.5 mA / cm 2 an image taken by SEM after Li deposition for 8 hours at a current density of 0.5 mA / cm

[0040] Figure 4 2-1 of Example 1 is an image taken by SEM after Li deposition for 7 minutes 30 seconds at a current density of 4.0 mA / cm 2 an image taken by SEM after Li deposition for 7 minutes 30 seconds at a current density of 4.0 mA / cm

[0041] Figure 4 2-2 of Example 1 is an image taken by SEM after Li deposition for 1 hour at a current density of 4.0 mA / cm 2 an image taken by SEM after Li deposition for 1 hour at a current density of 4.0 mA / cm

[0042] Figure 5 shows experimental results of coulombic efficiency measured at a current density of 0.5 mA / cm 2 of Example 1 and Comparative Examples 1 and 3 according to Experimental Example 2;

[0043] Figure 6 shows voltage profiles of the first coulombic efficiency test at 0.5 mA / cm 2 , 2.0 mA / cm 2 , and 3.0 mA / cm 2 of Comparative Examples 1 to 3 according to Experimental Example 3;

[0044] Figure 7 shows voltage profiles at the time of lithium deposition for 1 hour at a current density of 4.0 mA / cm 2 of Example 1 and 2 and Comparative Example 3 according to Experimental Example 4;

[0045] Figure 8 shows voltage profiles at the time of lithium deposition for 2 hours at a current density of 0.5 mA / cm 2 of Example 1, 3 to 5, and Comparative Example 3 according to Experimental Example 4; and

[0046] Figures 9 to 12 are upper surface and cross-sectional images taken by SEM after lithium deposition for 2 hours at a current density of 0.5 mA / cm 2 of Example 1 and Examples 3 to 5 according to Experimental Example 4. DETAILED DESCRIPTION

[0047] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION

[0048] The terms and words used in the present specification and claims should not be interpreted as being limited to the commonly used meanings or to dictionary definitions but should be interpreted in the context of the present invention based on the rules of interpretation of the terms and words together with the technical scope of the present disclosure. Accordingly, the embodiments described herein and the configurations shown in the drawings are merely the most preferred embodiments and do not represent all ideas of the present disclosure, and it should be understood that various equivalents and modifications can be made thereto without departing from the scope of the present invention.

[0049] According to one embodiment of the present disclosure, there is provided a negative current collector for a lithium metal battery, the negative current collector comprising: a metal current collector substrate, and a coating layer formed on at least one surface of the metal current collector substrate, the coating layer containing a ferroelectric, a metal material capable of alloying with lithium, a conductive material, and a binder.

[0050] In this case, the metal current collector substrate can be one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper subjected to surface treatment with a dissimilar metal, stainless steel subjected to surface treatment with a dissimilar metal, and an aluminum-cadmium alloy, and specifically, it can be a metal containing copper.

[0051] The present inventors recognized the problem of lithium metal batteries and conducted intensive research on a fundamental method capable of inhibiting lithium dendrite formation, and as a result, it was confirmed that when a composite coating layer containing a material capable of interacting with lithium ions to increase the concentration of lithium ions on the surface of the negative current collector, and a material capable of serving as a seed for a lithium metal nucleus is formed on the surface of the current collector, effective inhibition of lithium dendrite formation is achieved, thereby completing the present disclosure.

[0052] Specifically, the present inventors confirmed that a typical material capable of interacting with lithium ions is a dielectric material having polarity, and in the case of a ferroelectric material, it has a very large polarity characteristic compared to a general dielectric material, and thus has excellent interaction with ions. In addition, since a metal material capable of alloying with lithium (Li) exists as a material capable of serving as a seed for a Li metal nucleus, a coating layer can be formed using the two materials described above, thereby obtaining the effect of the present disclosure.

[0053] However, in addition, in order to form such a coating layer, a vapor deposition method such as CVD can be used, but the present inventors confirmed that such a production method has problems of being expensive, coating layer formation being slow, and a side reaction possibly occurring between the two materials, and thus a production method capable of solving the side reaction between the two materials and the high manufacturing price was researched, and it was recognized that if these problem points are solved, it can be commercialized as a negative electrode current collector for a lithium metal battery.

[0054] In addition, the present inventors recognized that in addition to the coating layer formation method, the binding force between the coating layer and the current collector is also important, and when the binding force between the coating layer and the electrode is low, peeling of the coating layer occurs in the electrolyte, and thus it is necessary to form a strong binding force between the coating layer and the electrode, and thus the present disclosure was completed.

[0055] Specifically, the coating layer formed on the negative electrode current collector according to the present disclosure can contain 70 to 89 parts by weight of a ferroelectric, 3 to 10 parts by weight of a metal material alloyed with lithium, 3 to 10 parts by weight of a conductive material, and 5 to 20 parts by weight of a binder, based on 100 parts by weight of the coating layer. More specifically, the coating layer can contain 75 to 85 parts by weight of a ferroelectric, 3 to 10 parts by weight of a metal material alloyed with lithium, 5 to 10 parts by weight of a conductive material, and 5 to 15 parts by weight of a binder, based on 100 parts by weight of the coating layer.

[0056] When the above ranges are satisfied, the above binding force, interaction with lithium ions, and effects such as lithium nucleation seeds can be effectively achieved, and thus are preferred.

[0057] In this case, the ferroelectric can be at least one selected from the group consisting of organic ferroelectrics containing BaTiO3, KNbO3, NaTiO3, KTaO3, Pb(Zr,Ti)O3, SrBiTa2O9, BiTiO 12 , LiTaO3, LiNbO3, WO3, KH2PO4, or NaKC4H4O6·4H2O, while containing a polymer.

[0058] Specifically, it can be at least one selected from the group consisting of BaTiO3, Pb(Zr,Ti)O3, SrBiTa2O9, and BiTiO 12 , more specifically, it can be BaTiO3.

[0059] Further, the metal material capable of alloying with lithium can be at least one selected from the group consisting of Si, Ge, Sn, Pb, Bi, Sb, As, P, Au, Ag, Zn, Al, and oxides thereof. Specifically, it can be at least one selected from the group consisting of Si, Ge, Sn, Ag, and oxides thereof, more specifically, it can be at least one selected from the group consisting of Si, Ge, and oxides thereof. Most specifically, it can be Si, which is most preferably used for the role of a seed and can be conveniently used.

[0060] On the other hand, in this case, the particle size (D50) of the metal material capable of alloying with lithium can be 10 nm to 10 μm. That is, particles of various sizes can be used, and a more preferable particle size can be selected depending on the metal material capable of alloying with lithium used. For example, in the case of Si, the particle size (D50) thereof can be 0.1 to 1 μm, and in the case of Sn, the particle size (D50) thereof can be 50 to 400 nm.

[0061] The particle size (D50) refers to the particle size (diameter) at the point of 50% in the particle number cumulative distribution with respect to the particle size. That is, D50 is the particle size at the point of 50% in the particle number cumulative distribution with respect to the particle size.

[0062] D50 can be measured by using a laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). When the particles pass through a laser beam, the diffraction pattern difference according to the particle size is measured to calculate the particle size distribution. D50 can be measured by calculating the particle size corresponding to the point of 50% in the particle number cumulative distribution with respect to the particle size in the analyzer.

[0063] The electrically conductive material is not particularly limited as long as it has high electrical conductivity and does not cause chemical changes in the corresponding battery, and for example, graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal crack black; electrically conductive fibers such as carbon fibers and metal fibers; metal powders such as fluorocarbon powders, aluminum powders, and nickel powders; electrically conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; electrically conductive metal oxides such as titanium oxides; and electrically conductive materials such as polyphenylene derivatives can be used.

[0064] Specific examples of commercially available conductive materials include: acetylene black series products available from Chevron Chemical Company, Denka black available from Denka Singapore Private Limited, Gulf Oil Company, Ketjen black available from Armak Company, EC series products, Vulcan XC-72 available from Cabot Company, and Super P available from Timcal Company, etc.

[0065] Each binder is a binder type known in the art, and is not limited as long as it is a type capable of improving the adhesion of the electrode components. Examples thereof can be at least one selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, fluoro rubber, polyacrylic acid (PAA) as an aqueous binder, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC). Specifically, it can be an aqueous binder, more specifically, a polyacrylic acid (PAA) aqueous binder.

[0066] On the other hand, the coating layer can be formed to a thickness of 1 to 10 μm, specifically 2 to 5 μm.

[0067] When the thickness is outside the above range and too thin, it is difficult to achieve the intended effects as much as the present application, and when the thickness is too thick, the increase in effect is reduced and the overall volume is increased, so that the energy density per volume or the like can be reduced, and thus is not preferable.

[0068] On the other hand, according to another embodiment of the present disclosure, there is provided a method of manufacturing the negative electrode current collector, the method including the steps of:

[0069] (a) mixing a powdered ferroelectric, a metal material capable of alloying with lithium, and a conductive material to prepare a mixture;

[0070] (b) mixing an aqueous binder with the mixture to prepare a coating slurry;

[0071] (c) applying the coating slurry to the metal current collector substrate; and

[0072] (d) performing primary drying of the metal current collector substrate coated with the coating slurry in an air atmosphere, and performing secondary drying thereof in a vacuum atmosphere.

[0073] That is, according to the present application, as described above, the present disclosure forms a coating layer in the form of a slurry as a very simple method, rather than forming a coating layer by a method such as vapor deposition.

[0074] In this case, in step (a), the kinds and mixing ratio of the powdered ferroelectric, the metal material capable of alloying with lithium, and the conductive material can be mixed in the same ratio as contained in the coating layer described above.

[0075] Here, when the aqueous binder is further mixed in step (b), it can be mixed in the ratio described above. Examples of the aqueous binder are also as described above.

[0076] The method of coating the coating slurry in step (c) is not limited, and a conventional method of forming an active material layer of a lithium secondary battery can be similarly used. For example, coating can be performed by a method of casting using a doctor blade.

[0077] After that, the coating layer is formed by performing the primary and secondary drying of step (d).

[0078] The primary drying step can be a step of evaporating water by using the aqueous binder of the present disclosure, and then the secondary drying step is a step of removing solvents and impurities that can remain on the current collector substrate and the coating layer by heating to a higher temperature under a vacuum state.

[0079] Here, the primary drying can be performed, for example, by heating at 60 to 100°C for 3 to 8 hours, and the secondary drying can be performed, for example, by heating at 100 to 150°C for 6 to 24 hours.

[0080] On the other hand, according to another embodiment of the present disclosure, a lithium metal battery is provided, including: an electrode assembly including a negative electrode in which Li metal is deposited on a negative current collector according to the above-described embodiment, a positive electrode, and a separator interposed between the negative electrode and the positive electrode; and a lithium nonaqueous electrolyte.

[0081] When Li metal is deposited using the negative current collector according to the present disclosure, as Figure 1 illustrated, the metal material capable of alloying with lithium acts as a seed to cause a Si-Li alloy reaction, and then mainly forms large-sized Li particles together with the ferroelectric having a large polarity characteristic, centered on the Si-Li alloy.

[0082] Hereinafter, by using the negative current collector for a lithium metal battery according to the present disclosure having such a configuration, the electrochemical performance to be achieved by the present disclosure is analyzed and described.

[0083] [Example 1]

[0084] A BaTiO3 / Micro Si coating layer was formed on the surface of a copper current collector substrate.

[0085] 112.5 mg of powdered BaTiO3 (Samsung Electro-Mechanics), 7.5 mg of Micro Si (Sigma-Aldrich, D50: 0.1-1 μm), and 7.5 mg of super P (IMERYS) were mixed with a mortar and pestle.

[0086] Next, the mixture was mixed with 1.125 g of a PAA aqueous binder (2 wt%) and stirred in a vial for 6 hours. To minimize secondary particles, the secondary particles were crushed using the frictional force between the stirring rod and the surface of the vial. At this time, when it was confirmed that the viscosity of the coating slurry was thick, the concentration of the coating slurry was diluted by adding deionized water at 20 μL each time.

[0087] The organic and inorganic materials on the surface of a copper foil (Wellcos) having a thickness of 20 μm to be coated with the coating slurry were removed with deionized water and acetone.

[0088] The coating slurry was coated onto the cleaned copper foil, and then cast to a height of 12 μm with a doctor blade.

[0089] The slurry-coated electrode was dried at 80°C for 6 hours in an air atmosphere to volatilize the solvent, and then dried at 130°C for 12 hours in a vacuum atmosphere to remove the remaining solvent and impurities.

[0090] Through the above procedure, a BaTiO3 / Micro Si coating layer having a thickness of 3 to 5 μm was formed on the copper electrode to make a negative current collector. Figure 2 The upper surface of the formed BTO / Micro Si negative current collector was shown.

[0091] [Example 2]

[0092] A BaTiO3 / Micro Si coating layer was formed on the surface of a copper current collector substrate.

[0093] 105 mg of powdered BaTiO3 (Samsung Electro-Mechanics), 15 mg of Micro Si (Sigma-Aldrich, D50: 0.1-1 μm), and 15 mg of Super P (IMERYS) were mixed with a mortar and pestle.

[0094] Next, the mixture was mixed with 0.75 g of a PAA aqueous binder (2 wt%) and stirred in a vial for 6 hours. Except for these points, the negative current collector was made in the same manner as in Example 1.

[0095] [Example 3]

[0096] A BaTiO3 / Micro Ge coating layer was formed on the surface of a copper current collector substrate.

[0097] 112.5 mg of powdered BaTiO3 (Samsung Electro-Mechanics), 7.5 mg of Micro Ge (Sigma-Aldrich, D50: 0.1-1 μm), and 7.5 mg of Super P (IMERYS) were mixed with a mortar and pestle.

[0098] Next, the mixture was mixed with 1.125 g of a PAA aqueous binder (2 wt%), and then stirred in a vial for 6 hours. Except for these points, a negative electrode current collector was fabricated in the same manner as Example 1.

[0099] [Example 4]

[0100] A BaTiO3 / Nano Sn coating layer was formed on the surface of a copper current collector substrate.

[0101] 112.5 mg of powdered BaTiO3 (Samsung Electro-Mechanics), 7.5 mg of Nano Sn (Sigma-Aldrich, D50: 50-400 nm), and 7.5 mg of Super P (IMERYS) were mixed with a mortar and pestle.

[0102] Next, the mixture was mixed with 1.125 g of a PAA aqueous binder (2 wt%), and then stirred in a vial for 6 hours. Except for these points, a negative electrode current collector was fabricated in the same manner as Example 1.

[0103] [Example 5]

[0104] A BaTiO3 / Nano SnO2coating layer was formed on the surface of a copper current collector substrate.

[0105] 112.5 mg of powdered BaTiO3 (Samsung Electro-Mechanics), 7.5 mg of Nano SnO2(Sigma-Aldrich, D50: 30-200 nm), and 7.5 mg of Super P (IMERYS) were mixed with a mortar and pestle.

[0106] Next, the mixture was mixed with 1.125 g of a PAA aqueous binder (2 wt%), and then stirred in a vial for 6 hours. Except for these points, a negative electrode current collector was fabricated in the same manner as Example 1.

[0107] [Comparative Example 1]

[0108] The surface of a 20-μm-thick electrode copper foil (Wellcos Co.) was not subjected to coating treatment. Inorganic / organic materials were removed with deionized water and acetone, and then dried in a vacuum atmosphere at 130°C for 12 hours. Other than these, the experimental conditions were the same as in Example 1.

[0109] [Comparative Example 2]

[0110] A dielectric material, Al2O3, was used to form a coating on the surface of a 20-μm-thick electrode copper foil (Wellcos Co.).

[0111] Specifically, powdered Al2O3 (Sigma-Aldrich Co., D50: 0.1-1 μm) was pulverized using a planetary ball mill. In a ZrO2 container, ZrO2 balls having diameters of 0.5 mm and 1.0 mm were mixed in a volume ratio of 2:1:1, and then acetone was added and the mixture was pulverized at 500 rpm for 10 hours. Then, the ZrO2 balls were filtered through a sieve and heated to 120°C in an air atmosphere using a hot plate.

[0112] 120 mg of the pulverized Al2O3 and 7.5 mg of Super P (IMERYS Co.) were mixed in a mortar and pestle.

[0113] Next, the mixture was mixed with 1.5 g of a PAA aqueous binder (2% by weight) and stirred in a vial for 6 hours. To minimize secondary particles, the secondary particles were pulverized using the frictional force between the stirring rod and the surface of the vial. At this time, when it was confirmed that the viscosity of the coating slurry was thick, the concentration of the coating slurry was diluted by adding deionized water at 20 μL each time.

[0114] However, when the viscosity of the coating slurry was very thick, a Thinky mixer was used. The coating slurry was put into a Thinky container, and then 1 mm ZrO2 balls 5EA were added and the secondary particles were pulverized. Mixing was performed at 2000 RPM for 2 minutes each time, and the viscosity was adjusted by adding 20 μL of deionized water. After the viscosity was adjusted, the mixture was mixed at 2000 RPM for 20 minutes.

[0115] The 20-μm-thick electrode copper foil (Wellcos Co.) on the surface of which the organic and inorganic materials were to be coated with the mixed slurry was removed with deionized water and acetone.

[0116] The coating slurry was applied to the cleaned copper foil, and then cast to a height of 12 μm using a doctor blade.

[0117] The slurry-coated electrode was dried in an air atmosphere at 80°C for 6 hours to volatilize the solvent, and then it was dried in a vacuum atmosphere at 130°C for 12 hours to remove the remaining solvent and impurities.

[0118] By the above procedure, an Al2O3 coating layer having a thickness of 3 to 5 μm was formed on the copper electrode, and a negative electrode current collector was produced.

[0119] [Comparative Example 3]

[0120] A BaTiO3 coating layer was formed on the surface of the copper current collector substrate.

[0121] 112.5 mg of powdered BaTiO3 (Samsung Electro-Mechanics, 300 to 400 nm) and 7.5 mg of Super P (IMERYS Corporation) were mixed with a mortar and pestle.

[0122] Next, the mixture was mixed with 1.5 g of a PAA aqueous binder (2 wt%) and stirred in a vial for 6 hours. Except for these points, a negative electrode current collector was produced in the same manner as in Example 1.

[0123] [Experimental Example 1]

[0124] Lithium Deposition and Structure Evaluation

[0125] To confirm the structure of lithium deposition and vapor-deposited lithium using the negative electrode current collector produced according to Example 1 and Comparative Example 3, SEM photographs were taken and analyzed, and the results are shown in FIGS. 1 and 2, respectively. Figure 3 and Figure 4

[0126] A negative electrode current collector having a diameter of 11 mm and Li metal having a diameter of 10 mm were used, and Li having a diameter of 10 mm was deposited on the surface of the negative electrode current collector. This is because when the size of the negative electrode current collector is smaller than the size of the lithium metal, a phenomenon in which lithium is deposited on the edge occurs, and thus the size of the negative electrode current collector is greater than the diameter of the lithium metal used.

[0127] At this time, the reaction area was 10 mm, which is the diameter of Li, and thus the current was calculated based on 10 mm. At this time, for a current density of 0.5 mA / cm 2 , Li deposition was performed for 1 hour and 8 hours, respectively, and for a current density of 4.0 mA / cm 2 , Li deposition was performed for 7 minutes and 30 seconds and 1 hour, respectively, and the amount of Li deposition was adjusted to 0.5 mAh / cm 2 and 4.0 mAh / cm 2 , and thus Li was formed on the negative electrode current collector.

[0128] In this case, 1 wt% of LiNO3 was added to an electrolyte in which 1 M LiTFSI was dissolved in a solvent in which DOL (1,3-dioxolane):DME (1,2-dimethoxyethane) was 1:1 in volume / volume ratio, and used as an electrolyte.​

[0129] Subsequently, to observe the deposition behavior of Li, the cell was disassembled, the lithium deposition sample was recovered, cleaned with a DOL (1,3-dioxolane) volatile solvent for 1 minute in an Ar atmosphere glove box, and then the solvent was evaporated. To minimize the reaction of the deposited lithium with external air in order to image the recovered sample by SEM, the sample was placed in an Ar-filled vial until just before SEM imaging to minimize exposure to air. Several points near the center of the deposited Li were arbitrarily selected and measured, and representative images were obtained.

[0130] Figure 3 The shape of lithium deposition on the negative current collector coated with only BTO according to Comparative Example 3 is shown. Specifically, Figure 3 1-1 is an image taken by SEM after Li deposition for 1 hour at a current density of 0.5 mA / cm 2 Figure 3 1-2 is an image taken by SEM after Li deposition for 8 hours at a current density of 0.5 mA / cm 2 Figure 3 2-1 is an image taken by SEM after Li deposition for 7 minutes and 30 seconds at a current density of 4.0 mA / cm 2 Figure 3 2-2 is an image taken by SEM after Li deposition for 1 hour at a current density of 4.0 mA / cm 2

[0131] Figure 4 The shape of Li deposition on the negative current collector coated with BTO / Micro Si according to Example 1 is shown. Specifically, Figure 4 1-1 is an image taken by SEM after Li deposition for 1 hour at a current density of 0.5 mA / cm 2 Figure 4 1-2 is an image taken by SEM after Li deposition for 8 hours at a current density of 0.5 mA / cm 2 Figure 4 2-1 is an image taken by SEM after Li deposition for 7 minutes and 30 seconds at a current density of 4.0 mA / cm 2 Figure 4 2-2 is an image taken by SEM after Li deposition for 1 hour at a current density of 4.0 mA / cm 2

[0132] Referring to Figure 3 ​​​​​​​​In the case of the BTO-coated sample, small Li clusters composed of elongated Li were formed at the initial stage of Li deposition, and then they grew and aggregated to form a dense Li structure. This was similarly shown in Comparative Example 1 in which no coating was formed.

[0133] However, it was confirmed that, at a current density of 4.0 mA / cm 2 , small Li nuclei were densely formed on the entire surface of the copper electrode at the initial stage of Li deposition in the case of the negative current collector without forming a coating, and then they grew in the vertical direction to form a porous Li structure.

[0134] On the other hand, with reference to Figure 3 and 4 , at a current density of 4.0 mA / cm 2 , small elongated Li clusters were formed at the initial stage of Li deposition in the case of the negative current collector coated with BTO, and then they grew and aggregated to form a denser Li structure than in the case of the copper current collector electrode.

[0135] However, it was confirmed that, at a current density of 4.0 mA / cm 2 , a Si-Li alloy reaction occurred at the initial stage of lithium deposition in the case of the negative current collector coated with BTO / Si, and then large-sized Li particles were formed mainly around the Si-Li alloy.

[0136] [Experimental Example 2]

[0137] Electrochemical Performance Evaluation

[0138] The electrochemical property evaluation of the lithium metal battery using the negative current collector prepared according to Example 1 and Comparative Examples 1 and 3, as manufactured in Experimental Example 1, was performed using a constant current method. After Li deposition was performed at 1.0 mAh / cm 2 , Li desorption was performed at the same current density until a voltage of 0.5 V was reached, and the ratio of the amount of desorbed Li to the deposited Li (coulombic efficiency) was analyzed. The current density was performed at a strength of 0.5 mA / cm 2 , 2.0 mA / cm 2 , and 3.0 mA / cm 2 at room temperature.

[0139] The results of the electrochemical property evaluation according to the cycle of the negative current collector prepared according to Example 1 and Comparative Examples 1 and 3 are shown in Figure 5 and Table 1 below.

[0140] [Table 1]

[0141]

[0142] As shown in Table 1, it can be confirmed that when using the negative current collector prepared according to Example 1, in which the coating of the present disclosure is formed, and the negative current collector prepared according to Comparative Example 3, based on 0.5 mA / cm 2 The coulombic efficiency after 100 cycles was 97.66% and 98.51%, which is more than 14% higher than that of Comparative Example 1.

[0143] Observation based on 2.0 mA / cm 2 The coulombic efficiency after 100 cycles was confirmed to be 94.39% and 95.96%, which is more than 11% higher than that of Comparative Example 1.

[0144] Observation based on 3.0 mA / cm 2 The coulombic efficiency after 100 cycles was confirmed to be 95.08% and 97.39%, which is more than 17% higher than that of Comparative Example 1.

[0145] However, it can be confirmed that the improvement rate is higher when the coating also contains Si (Example 1) compared to when only BTO is contained in the coating (Comparative Example 3).

[0146] In addition, such as Figure 5 As shown, it can be confirmed that in the case of the sample having the coating formed according to Example 1, it is stable compared to Comparative Example 1 without a coating and Comparative Example 3 with a coating containing only BTO, and the overall average coulombic efficiency increases. It can be seen that as the number of cycles increases, this trend becomes more significant in the order of Comparative Example 1 < Comparative Example 3 < Example 1.

[0147] [Experiment Example 3]

[0148] Coating Effect Analysis - Effect of Ferroelectric Material

[0149] To confirm the effectiveness of the ferroelectric material contained in the coating used, the capacitance measuring the amount of ions accumulated on the electrode surface was measured. A single cell was formed using a negative electrode current collector with a diameter of 11 mm formed by the method of Comparative Examples 1 to 3, and Li metal as the counter electrode, with a separator added to prevent short circuit between the two electrodes.

[0150] A current of 50 μA was applied to the single cell until the voltage dropped from 0 V to 1.5 V, during which the capacitance during the discharge step was measured to determine the capacitance accumulated on the surface of the current collector electrode. In Comparative Example 1, since it was a pure current collector without a coating, the capacitance per unit weight could not be measured. Therefore, the area capacitance was measured as follows.

[0151] C (area capacitance) = (I × Δt) / (A × ΔV)

[0152] I: current size, At: charge (discharge) time, A: electrode cross-sectional area, ΔV: voltage range

[0153] [Table 2]

[0154]

[0155] As can be seen from Table 2, it is confirmed that the measured capacitance size follows the order of BaTiO3 coating > Al2O3 coating > Coating X, and the trend of the measured values is identical to the polarity size.

[0156] That is, it can be seen that due to the high polarity characteristics of BaTiO3, a high ion concentration region is formed around the electrode.

[0157] Similarly, Figure 6 The Li deposition voltage curves according to the current density when using Comparative Examples 1 to 3 are shown. As can be seen from Figure 6 it is confirmed that in the case of Comparative Example 3, a large Li nucleation under-potential occurs at the initial Li nucleation stage compared to Comparative Example 1. This is because Li nucleation is difficult to occur due to the insulating layer coated on the current collector substrate. Unusually, in the case of Comparative Example 3, it is confirmed that the under-potential is quickly recovered, and the under-potential at the Li growth stage is even smaller compared to Comparative Example 1. In the case of Comparative Example 2 using a dielectric material, it is confirmed that the under-potential is greater than Comparative Example 1 both in the Li nucleation step and the Li growth step. In summary, due to the high polarity characteristics of BaTiO3, a high Li ion concentration region is formed around the electrode, which can alleviate the ion depletion region. Therefore, even at a high current density, the Li growth behavior exhibits similar growth behavior to the current density condition of 0.5 mA / cm 2 , instead of dendritic growth causing a porous structure, thereby enabling the formation of a dense Li structure. As can be seen from this, as a dielectric, the capacitance linearly increases with the increase in the dielectric constant, and thus using a ferroelectric can exhibit a more superior effect than using a general dielectric. It is concluded that when a ferroelectric with a dielectric constant similar to BTO is used, the effects of the present application can be achieved.

[0158] [Experimental Example 4]

[0159] Coating Effect Analysis - Effect of Metal Material Capable of Alloying with Lithium

[0160] To confirm the effectiveness of the Si material contained in the coating used, the Si weight percentage of the BTO / Si coating was adjusted, and the lithium deposition experiment and the voltage curve at that time were confirmed. That is, a single cell was constructed using an 11 mm diameter negative electrode current collector formed by the methods of Comparative Example 3 and Examples 1 and 2, using Li metal as the counter electrode and adding a separator to prevent short circuit between the two electrodes.

[0161] To analyze the underpotential during the Li nucleation and growth stages, at 4.0 mA / cm²... 2 At a current density of 4.0 mAh / cm³, deposition was achieved in 1 hour. 2 The nucleation underpotential of Li was analyzed from the measured voltage curve to confirm the nucleation underpotential based on weight % . The results are as follows Figure 7 As shown.

[0162] from Figure 7 As shown, it was confirmed that the Li underpotential during the nucleation step decreased with increasing Si weight % in the BTO / Si coating, and its underpotential was lower than that of Comparative Example 3 without Si. In other words, when Si is included, the nucleation underpotential decreases, and the rate of decrease appears to increase with increasing Si content. Therefore, it can be explained that the Si contained in the coating acts as Li nucleation sites.

[0163] Furthermore, to confirm the effectiveness of the lithium-alloyable metal material contained in the coating, the lithium-alloyable metal material (Ge, Sn, SnO2) was changed, and the lithium deposition experiment and the voltage curve at that time were confirmed. That is, a single cell was constructed by using a negative electrode current collector with a diameter of 11 mm formed by the methods of Comparative Example 3, Example 1, and Examples 3 to 5, using Li metal as the counter electrode, and adding a separator to prevent short circuit between the two electrodes.

[0164] To analyze the underpotential during the Li nucleation and growth stages, at 0.5 mA / cm²... 2 At a current density of 1.0 mAh / cm³, deposition was performed over 2 hours. 2 The Li nucleation underpotential was analyzed in the measured voltage curve, and the results are as follows: Figure 8 As shown, SEM images reveal the top surface and cross-section of the Li deposition shape. Figures 9 to 12 As shown.

[0165] Reference Figure 8 It can be confirmed that the underpotentials of Sn, SnO2, Ge, and Si are all smaller than those of Comparative Example 3, which does not contain Si. Furthermore, the nucleation underpotential is reduced the most when Si and Ge are included, while the reduction is less for Sn and SnO2 than for Si or Ge, but it is still greater than that for Comparative Example 3.

[0166] On the other hand, refer toFigures 9 to 12 It was confirmed that when Si or Ge is added, it also acts as a Li nucleation site, thus inducing lithium deposition into the BTO / Si layer or BTO / Ge layer. In this case, it was also confirmed that the Li underpotential in the nucleation step is reduced.

[0167] On the other hand, it was confirmed that when a small particle size material such as Sn or SnO2 is added, internal deposition is suppressed and spherical Li is mainly deposited on the upper part of the coating. Thus, from Figure 8 It was confirmed that although the Li underpotential in the nucleation step is reduced, it is not as effective as Si or Ge.

[0168] From the results of the examples as described above, according to the method of the present disclosure, due to the high polar characteristics of the ferroelectric and the interaction between lithium ions, a high lithium ion concentration region is formed around the electrode and lithium nucleation sites are formed from metal materials that can alloy with lithium, thus obtaining an improved electrochemical lithium deposition behavior, and the formation of a dense lithium deposition structure resulting therefrom, and an improved and stable coulombic efficiency, even under high current density conditions.

[0169] In addition, the method according to the present disclosure has the advantages of low cost and high productivity due to the slurry casting process, and a simple process suitable for mass production.

[0170]

Industrial applicability

[0171] The negative current collector according to the present disclosure forms a high concentration of Li ions around the electrode through the interaction between the ferroelectric material and Li ions. Also, metal materials that can alloy with lithium (that cause a reaction with Li alloying) act as nucleation seeds, reducing the underpotential required for nucleation, and can form a dense Li structure with a 3D structure and improve the electrochemical performance.

[0172] In addition, since the coating is prepared in the form of a slurry according to the present disclosure, compared to conventional coating processes such as deposition, process costs and time can be reduced, thus having the advantage of being suitable for mass production.

Claims

1. A lithium metal battery comprising: an electrode assembly comprising a negative electrode in which Li metal is deposited on a negative current collector, a positive electrode, and a separator interposed between the negative electrode and the positive electrode, and a lithium nonaqueous electrolyte, wherein the negative current collector comprises: a metal current collector substrate, and a coating layer formed on at least one surface of the metal current collector substrate, the coating layer containing, based on 100 parts by weight of the coating layer, 75 to 85 parts by weight of a ferroelectric, 3 to 10 parts by weight of a material capable of alloying with lithium, 5 to 10 parts by weight of an electrically conductive material, and 5 to 15 parts by weight of a binder, wherein the material capable of alloying with lithium is at least one selected from the group consisting of Si, Ge, Sn, Pb, Bi, Sb, As, P, Au, Ag, Zn, Al, and oxides thereof, and wherein the coating layer is formed to a thickness of 1 to 5 micrometers.

2. The lithium metal battery according to claim 1, wherein: the metal current collector substrate is one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper subjected to surface treatment with a dissimilar metal, stainless steel subjected to surface treatment with a dissimilar metal, and an aluminum-cadmium alloy.

3. The lithium metal battery according to claim 1, wherein: the metal current collector substrate is a metal comprising copper.

4. The lithium metal battery according to claim 1, wherein: the ferroelectric is at least one selected from the group consisting of organic ferroelectrics containing a polymer while also containing: BaTiO3, KNbO3, NaTiO3, KTaO3, Pb(Zr,Ti)O3, SrBiTa2O9, BiTiO 12 , LiTaO3, LiNbO3, WO3, KH2PO4, or NaKC4H4O6-4H2O.

5. The lithium metal battery according to claim 1, wherein: the material capable of alloying with lithium is at least one selected from the group consisting of Si, Ge, and oxides thereof.

6. The lithium metal battery according to claim 1, wherein: the material capable of alloying with lithium has a particle size D50 of 10 nanometers to 10 micrometers.

7. The lithium metal battery according to claim 1, wherein: the binder is a polyacrylic acid (PAA) aqueous binder.

8. A method of manufacturing the lithium metal battery according to claim 1, the method comprising the steps of: (a) mixing a powdered ferroelectric, a material capable of alloying with lithium, and an electrically conductive material to prepare a mixture, wherein the material capable of alloying with lithium is at least one selected from the group consisting of Si, Ge, Sn, Pb, Bi, Sb, As, P, Au, Ag, Zn, Al, and oxides thereof; (b) mixing an aqueous binder with the mixture to prepare a coating slurry; (c) applying the coating slurry to the metal current collector substrate; and (d) subjecting the metal current collector substrate coated with the coating slurry to primary drying in an air atmosphere and secondary drying in a vacuum atmosphere, thereby forming a coating layer, wherein the coating layer has a thickness of 1 to 5 micrometers.

9. The method of manufacturing a lithium metal battery according to claim 8, wherein: the ferroelectric is at least one selected from the group consisting of organic ferroelectrics containing a polymer while also containing: ​ BaTiO3, KNbO 3、 NaTiO3, KTaO3, Pb(Zr,Ti)O3, SrBiTa2O9, BiTiO 12 LiTaO3, LiNbO3, WO3, KH2PO4, or NaKC4H4O6-4H2O.

10. The method of manufacturing a lithium metal battery of claim 8, wherein: the aqueous binder is a polyacrylic acid (PAA) binder.

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